Description of artefacts in the PowerPlex Y23(®) system associated with excessive quantities of background female DNA

Male on female sexual assault cases that involve azoospermic individuals, those where the male has penetrated but failed to ejaculate, those where there has been an extended interval between the sexual assault and sample collection or where there has been only digital penetration are often difficult to investigate by employing traditional autosomal STR testing. Such cases often involve minimal amounts of male DNA either being deposited initially or remaining after the passage of time. These cases are often further complicated by the presence of large amounts of female DNA compared to the relatively small amounts of male DNA on the intimate samples taken. Y-STR kits provide a solution that allows targeting of male DNA in a mixed male/female sample. However, large quantities of excess female DNA have the potential to generate non-specific artefact peaks. Here we characterise a number of previously reported artefacts observed in the PowerPlex(®) Y23 system. We demonstrate that some of these artefacts can impact on profile interpretation and that they are highly dependent on the levels of female DNA present. These artefacts have been characterised to assist practitioners with the interpretation of such samples.